topic 6.2

Question 1

what is the function of the arteries?

Answer 1

convey blood at high pressure from the ventricles to the tissues of the body

Question 2

what are artery walls composed of?

Answer 2

muscle and elastic fibres

Question 3

name the 3 layers of arteries

Answer 3

• tunica externa: tough outer layer of connective tissue
• tunica media: thick layer containing smooth muscle and elastic fibres made of the protein elastin
• tunica intima: a smooth endothelium forming the lining of the artery

Question 4

what is the role of the arterial muscle and elastic fibres?

Answer 4

to assist in maintaining blood pressure between pump cycles

Question 5

systolic pressure

Answer 5

the peak pressure reached in an artery

Question 6

diastolic pressure

Answer 6

the minimum pressure inside an artery

Question 7

general role of arterial elastic fibres in walls

Answer 7

allow the arterial wall to stretch and expand upon the flow of a pulse through the lumen

Question 8

role of elastic fibres in the maintenance of blood pressure

Answer 8

1. systolic pressure pushes the wall of the artery outwards, widening the lumen and stretching elastic fibres in the wall, thus storing potential energy
2. at the end of each heartbeat the pressure in the arteries falls sufficiently for the stretched elastic fibres to squeeze the blood in the lumen.

This mechanism saves energy and prevents the diastolic pressure from becoming too low.

Question 9

general role of arterial muscle fibres in walls

Answer 9

help to form a rigid arterial wall that is capable of withstanding the high blood pressure without rupturing

Question 10

role of muscle fibres in the maintenance of blood pressure

Answer 10

VASOCONSTRICTION
circular muscles in the wall form a ring so when they contract, the circumference is reduced and the lumen is narrowed, blood pressure increase

Question 11

why do arterioles have a particularly high density of muscle cells?

Answer 11

so that they can respond to various hormone and neural signals to control blood flow to downstream tissues

Question 12

artery:
- diameter
- relative thickness of wall and diameter of lumen
- number of layers in wall
- muscle and elastic fibres in wall
- valves

Answer 12

• larger than 10µm
• relatively thick wall and narrow lumen
• 3
• abundant
• none

Question 13

what is the role of capillaries?

Answer 13

to allow exchange of materials between cells in tissues and the blood in the capillary

Question 14

give 2 tissues that do not contain capillaries

Answer 14

tissues of the lens and cornea in the eye- these must be transparent

Question 15

state and explain the adaptations of capillaries

Answer 15

• very small diameter which allows passage of only a single red blood cell at a time (optimal exchange)
• capillary wall is made of a single layer of cells to minimise the diffusion distance for permeable materials
• surrounded by a basement membrane which is permeable to necessary materials
• may contain pores to further aid in the transport of materials between tissue fluid and blood

Question 16

describe plasma and tissue fluid

Answer 16

plasma is the fluid in which blood cells are suspended; tissue fluid contains oxygen, glucose, and all other substances in blood plasma apart from large protein molecules which cannot pass through capillary wall

Question 17

describe the process of absorption from capillaries into tissues

Answer 17

fluid flows between the cells in a tissue, allowing the cells to absorb useful substances and excrete waste products as the tissue fluid then re-enters the capillary network

Question 18

describe how capillary structure may vary depending on its location in the body and specific role

Answer 18

• wall may be continuous (eg nervous tissue in blood-brain barrier) with endothelial cells held together by tight junctions to limit permeability of large molecules
• In tissues specialised for absorption (e.g. intestines, kidneys), the capillary wall may be fenestrated (contains pores)
• some capillaries are sinusoidal and have open spaces between cells and be permeable to large molecules and cells (e.g. in liver)

Question 19

Arteries split into ? which in turn split into ?, decreasing arterial pressure as total vessel volume is ?

The branching of arteries into capillaries therefore ensures blood is moving ? and all cells are located near a blood supply

After material exchange has occurred, capillaries will pool into ? which will in turn collate into larger ?

Answer 19

arterioles; capillaries; increased;

slowly;

venules; veins

Question 20

describe the flow of blood in capillaries

Answer 20

1. blood flows through the capillaries very slowly and at a very low pressure in order to allow for maximal material exchange
2. The higher hydrostatic pressure at the arteriole end of the capillary forces material from the bloodstream into the tissue fluid
3. The lower hydrostatic pressure at the venule end of the capillary allows materials from the tissues to enter the bloodstream

Question 21

capillary:
- diameter
- relative thickness of wall and diameter of lumen
- number of layers in wall
- muscle and elastic fibres in wall
- valves

Answer 21

• around 10µm
• extremely thin wall
• only one layer, tunica intimate which is an endothelium consisting of a single layer of very thin cells
• none
• none

Question 22

what is the role of veins?

Answer 22

to collect blood at low pressure from the tissues of the body and return it to the atria of the heart

Question 23

why is the hepatic portal vein unusual

Answer 23

it carries blood from stomach and intestines to liver, not back to the heart

Question 24

adaptations of veins

Answer 24

• very wide lumen (relative to wall thickness) to maximise blood flow for more effective return
• thin wall containing less muscle and elastic fibres as blood is flowing at a very low pressure
• pressure is low so veins possess valves to prevent backflow and stop the blood from pooling at the lowest extremities

Question 25

why do veins typically pass between skeletal muscle groups?

Answer 25

as they facilitate venous blood flow via periodic contractions; it would otherwise be difficult for the blood to move against the downward force of gravity

Question 26

describe how valves in veins work

Answer 26

• if blood starts to go backwards, it gets caught in the flaps of the pocket valve, which will with blood, blocking the lumen of the vein
• when blood flows towards the heart, it pushes the flaps to the sides of the vein so the pocket valve opens

Question 27

vein:
- diameter
- relative thickness of wall and diameter of lumen
- number of layers in wall
- muscle and elastic fibres in wall
- valves

Answer 27

• variable but much larger than 10
• relatively thin wall with variable but often wide lumen
• three layers
• small amounts
• present in many veins

Question 28

what is meant by the term ‘double circulation’?

Answer 28

in humans there is a separate circulation for the lungs:
- pulmonary circulation, to and from the lungs
- systemic circulation, to and from all other organs including the heart muscles

Question 29

why do humans have double circulation?

Answer 29

blood capillaries in the lungs cannot withstand high pressures so blood is pumped to them at relatively low pressure; after passing through the lung capillaries, pressure is still low so blood must return to the heart to be pumped again before it goes to other organs

Question 30

draw and label a diagram of a heart

Question 31

The contraction of the heart is called ? while the relaxation of the heart is called ?

Answer 31

systole; diastole

Question 32

Atrial systole is the period when

Ventricular systole is when

Answer 32

the atria are contracting

the ventricles are contracting

Question 33

Functions of atrial and ventricular systole

Answer 33

Atrial systole forces blood from the atria into the ventricles

During ventricular systole, blood is forced from the ventricles into the pulmonary artery and aorta

Question 34

Initiation of the heartbeat by the sinoatrial node

Answer 34

1. the heart beat is initiated by a group of cells in the wall of the right atrium called the sinoatrial node (SAN)
2. the cells of the sinoatrial node depolarise, reversing the charge across their membranes
3. Depolarisation of the cells in the sinoatrial node sends an electrical signal over the atria, causing them to contract in atrial systole
4. The electrical signal then reaches a region of non-conducting tissue which prevents it from spreading straight to the ventricles; this causes the signal to pause for around 0.1 s
   This delay means that the atria can complete their contraction before the ventricles begin to contract
5. The electrical signal is carried to the ventricles via the atrioventricular node (AVN), a region of conducting tissue between atria and ventricles
6. The signal then travels to the base of the heart via conductive fibres in the septum known as the bundle of His
7. it is then carried through conductive fibres called Purkyne fibres which spread around the sides of the ventricles, causing contraction of the ventricles from the apex, or base, of the heart upwards
8. Blood is forced out of the heart into the pulmonary artery and aorta

Question 35

why is the sinoatrial node is considered to be the pacemaker of the heart?

Answer 35

because it initiates the heart beat and so controls the speed at which the heart beats

Question 36

why is the heart considered myogenic?

Answer 36

it will beat without any external stimulus from other organs or the nervous system

Question 37

how can heart rate be increased or decreased?

Answer 37

with signals from branches of two nerves originating in the cardiovascular centre, a region in the medulla of the brain

• signals from one of the nerves cause the pacemaker to increase the frequency of heartbeats
• signals from the other decrease the rate

Question 38

low blood pressure, oxygen concentration and pH suggests that

High blood pressure, oxygen concentration and pH suggests that

Answer 38

the heart rate needs to speed up to increase the flow rate of blood to the tissues, deliver more oxygen and remove more CO2

the heart rate may need to slow down

Question 39

what is the function of epinephrine?

Answer 39

controlled by the brain, and increases the heart rate to prepare for vigorous physical activity because of a threat/opportunity

Question 40

what responds to the secretion of epinephrine by the adrenal glands?

Answer 40

the sinoatrial node

Question 41

describe Harvey’s discovery of the circulation of the blood with the heart acting as the pump

Answer 41

• demonstrated blood flow through larger vessels is unidirectional, with valves to prevent back flow
• showed the rate of flow through major vessels is too high for blood to be consumed in the body after being pumped out by the heart; it must therefore return to the heart and be recycled
• showed the heart pumps blood out in arteries and returns it in veins
• predicted presence of numerous fine vessels

Question 42

describe the events leading up to occlusion of the coronary arteries

Answer 42

1. Low density lipoproteins (LDL) containing fats and cholesterol accumulate in the artery wall of the coronary artery.
2. phagocytes are then attracted by signals from endothelium cells and smooth muscle. The phagocytes engulf the fats and cholesterol by endocytosis and grow very large.
3. Smooth muscle cells migrate to form a tough cap over the atheroma. The artery wall bulges into the lumen narrowing it and thus impeding blood flow.

Question 43

describe the possible effects of coronary artery occlusion

Answer 43

Coronary occlusion is a narrowing of the arteries that supply blood containing oxygen and nutrients to the heart muscle.

Lack of oxygen (anoxia) causes pain, known as angina, and impairs the muscle’s ability to contract, so the heart beats faster as it tries to maintain blood circulation with some of its muscle out of action.

The fibrous cap covering atheromas sometimes ruptures, which stimulates the formation of blood clots that can block arteries supplying blood to the heart and cause acute heart problems.

Question 44

give 6 factors that increase risk of atheroma

Answer 44

• high blood concentrations of LDL (low density lipoprotein)
• chronic high blood glucose concentrations, due to overeating, obesity or diabetes
• chronic high blood pressure due to smoking, stress or any other cause
• consumption of trans fats, which damage the endothelium of the artery.
• infection of the artery wall with Chlamydia pneumoniae
• production of trimethylamine N-oxide (TMAO) by microbes in the intestine.

Question 45

define atherosclerosis

Answer 45

the development of an atheroma - plaque, or fatty tissue that blocks arteries

Question 46

describe the pressure changes in the left atrium, left ventricle and aorta during the cardiac cycle using a diagram

Answer 46

0.0-0.1 seconds
The atria contract causing a rapid but relatively small pressure increase, which pumps blood from the atria to the ventricles, through the open atrioventricular valves.
The semilunar valves are closed and blood pressure in the arteries gradually drops to its minimum as blood continues to flow along them but no more is pumped in.

0.1-0.15 seconds
The ventricles contract, with a rapid pressure build up that causes the atrioventricular valves to close.
The semilunar valves remain closed.

0.15-0.4 seconds
The pressure in the ventricles rises above the pressure in the arteries so the semilunar valves open and blood is pumped from the ventricles into the arteries, transiently maximizing the arterial blood pressure.
Pressure slowly rises in the atria as blood drains into them from the veins and they fill.

0.4-0.45 seconds
The contraction of the ventricular muscles wanes and pressure inside the ventricles rapidly drops below the pressure in the arteries, causing the semilunar valves to close.
The atrioventricular valves remain closed.

0.45-0.8 seconds
Pressure in the ventricles drops below the pressure in the atria so the atrioventricular valves open.
Blood from the veins drains into the atria and from there into the ventricles, causing a slow increase in pressure.